Hot water recirculating systems are known in which the cooled down water content of the hot water distribution line is conveyed back into the hot water tank via a recirculation pipe as disclosed in the earlier U.S. Pat. No. 5,143,049. Modifying an existing water distribution system requires the installation of additional piping, which may be difficult to install. A different hot water recovery system is disclosed in U.S. Pat. No. 5,009,572 Imhoff et al. and U.S. Pat. No. 5,143,049 Laing, in which a recirculation pump is switched on if the hot water temperature near the faucet drops below a pre-determined level or as soon as a hot water faucet is opened. U.S. Pat. No. 5,277,219, Lund discloses a recirculation system in which the pump is activated by temperature sensors positioned near each hot water faucet. The pump conveys the cooled-down content of the hot water distribution line through the cold water distribution line back into the water heater. Thus the faucets in the distribution line receive warm water from the water heater when the cooled-down water content between the water heater and the faucets has been pumped into the cold water distribution line.
The aforesaid U.S. Pat. Nos. 5,009,572 Imhoff et al.; 5,143,049 Laing et al.; and 5,277,219 Lund are incorporated into this specification by this reference.
The prior art systems that recirculate the cooled-down portion of the hot water distribution line directly through the cold water distribution line have several drawback. The most serious is the fact that the system of Lund does not provide instant hot water because the pump does not start before the hot water faucet is turned on, so that hot water is only available when the hot water from the water heater has reached the faucet and has risen to the desired temperature. Indeed, the first volume of water coming from the hot water heater is cooled down by the cold water pipe, and a considerable amount of water must be drawn through the hot water faucet before that desired temperature is reach. A further disadvantage lies in the use of solenoids because they are expensive and prone to failure by lime deposits.
The present invention avoids these drawback.